U.S. patent application number 10/111990 was filed with the patent office on 2003-03-06 for method for measuring oscillation frequency of a fluid jet in a fluidic oscillator.
Invention is credited to Vannuffelen, Stephane.
Application Number | 20030041673 10/111990 |
Document ID | / |
Family ID | 8853953 |
Filed Date | 2003-03-06 |
United States Patent
Application |
20030041673 |
Kind Code |
A1 |
Vannuffelen, Stephane |
March 6, 2003 |
Method for measuring oscillation frequency of a fluid jet in a
fluidic oscillator
Abstract
The oscillation frequency of a fluid jet in a fluidic oscillator
is measured using a temperature sensor. The resistance of the
temperature sensor varies as a function of the oscillation of
frequency f.sub.0 of the jet. The method consists in feeding the
temperature sensor with an AC voltage of frequency f, and then in
determining the frequency components around the frequency 3.times.f
in the output signal from the temperature sensor in order to
determine the oscillation frequency f.sub.0 of the jet. The
frequency components in the signal output by the temperature sensor
are determined by measuring the measurement signal across the
terminals of the temperature sensor, then by synchronously
demodulating the measurement signal at the frequency 3.times.f, and
finally by determining the frequency of the demodulated measurement
signal, which frequency corresponds to the oscillation frequency
f.sub.0 of the jet.
Inventors: |
Vannuffelen, Stephane;
(Paris, FR) |
Correspondence
Address: |
Straub & Pokotylo
Suite 83
1 Bethany Road
Hazlet
NJ
07730
US
|
Family ID: |
8853953 |
Appl. No.: |
10/111990 |
Filed: |
August 20, 2002 |
PCT Filed: |
August 27, 2001 |
PCT NO: |
PCT/FR01/02670 |
Current U.S.
Class: |
73/861.19 |
Current CPC
Class: |
F15C 1/22 20130101; G01F
1/3227 20130101; G01F 1/3273 20220101 |
Class at
Publication: |
73/861.19 |
International
Class: |
G01F 001/20 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 1, 2000 |
FR |
00-11257 |
Claims
1. A method of measuring the oscillation frequency of a fluid jet
in a fluidic oscillator using a temperature sensor whose resistance
varies as a function of the oscillation frequency f.sub.0 of the
jet, said method consisting in: feeding the temperature sensor with
an AC voltage of frequency f; and determining the frequency
components around the frequency 3.times.f in the signal output by
the temperature sensor in order to determine the oscillation
frequency f.sub.0 of the jet.
2. A method of measuring the oscillation frequency of a fluid jet
in a fluidic oscillator using a temperature sensor in accordance
with claim 1, the method being characterized in that the frequency
components in the output signal from the temperature sensor are
determined by using the following steps: measuring the resulting
measurement signal V(t) across the terminals of the temperature
sensor; synchronously demodulating the measurement signal at the
frequency 3.times.f; and determining the frequency of the
demodulated measurement signal, which frequency corresponds to the
oscillation frequency f.sub.0 of the jet.
3. A method of measuring the oscillation frequency of a fluid jet
in a fluidic oscillator using a temperature sensor in accordance
with claim 2, characterized in that before the step of determining
the frequency of the measurement signal, the demodulated
measurement signal is filtered by means of a lowpass filter.
4. A method of measuring the oscillation frequency of a fluid jet
in a fluidic oscillator using a temperature sensor in accordance
with claim 2, characterized in that the step of synchronously
demodulating the measurement signal at the frequency 3.times.f, is
performed by multiplying the measurement signal V(t) by
cos(3.times.2.pi..times.f.time- s.t).
5. A method of measuring the oscillation frequency of a fluid jet
in a fluidic oscillator using a temperature sensor in accordance
with claim 1, characterized in that the frequency components of the
output signal from the temperature sensor and the oscillation
frequency f.sub.0 of the jet are determined by a fast Fourier
transform method.
Description
[0001] The invention relates to a method of measuring the
oscillation frequency of a fluid jet in a fluidic oscillator using
a temperature sensor whose temperature-dependent resistance varies
as a function of the oscillation frequency of the jet.
[0002] Fluidic oscillators are well known to the person skilled in
the art, and a particularly advantageous application thereof lies
in the field of measuring a fluid flow rate, as described in
document EP 0 882 951. A fluidic oscillator flowmeter 1, as shown
in an exploded view in FIG. 1, comprises a flowmeter body made up
of two side portions 2, 3 on either side of a central block 4 which
includes a measurement unit 5.
[0003] On the inside, the side portion 2 defines a "upstream"
chamber (not shown) into which the fluid penetrates after passing
through an inlet opening (not shown).
[0004] This chamber has a wall (not shown) in which the admission
opening is formed. This wall acts as a deflector wall and it
receives the impact of the fluid flow coming from the opening,
splitting the flow and deflecting it towards two orifices (only one
orifice 6 is visible in FIG. 1) formed in the deflection wall. Two
passages 7, 8 extend the orifices respectively and direct the fluid
flow fractions so as to make them converge on the inlet 9 of the
measurement unit 5. As a general rule, this inlet is in the form of
an elongate slot.
[0005] The measurement unit 5 has an oscillation chamber 10 in
which an obstacle 11 is positioned as shown by two arrows in FIG. 1
so as to face the inlet 9.
[0006] The fluid penetrating into the oscillation chamber and
encountering the front portion of the obstacle 11 oscillates
transversely relative to the direction A in a plane parallel to the
wall 12 and flows alternately past one end and the other end of
said obstacle so as to leave the oscillation chamber via the outlet
13 in the direction A. The inlet 9 and the outlet 13 of the
oscillation chamber are in alignment on the direction A. The
oscillation chamber 10 is defined firstly by the wall 12 and
secondly by another wall 15 parallel to said wall 12.
[0007] The flowmeter is installed between two pipes via flange
couplings included in the admission opening (not shown) and the
exhaust opening 14.
[0008] The fluid which leaves the oscillation chamber takes the
passage 16 which forms a bend so as to guide the fluid towards the
exhaust opening 14.
[0009] The side portion 2 is made integrally with the central block
4 of the flowmeter body which includes the measurement unit 5. The
other side portion 3 is manufactured separately and is subsequently
fitted onto the central block so as to act as a cover.
[0010] A cavity 17 is formed in the wall 15 so as to allow at least
one flow sensor to be installed therein, e.g. a temperature sensor
whose function is to detect the oscillations of the fluid in the
oscillation chamber 10. Thus, because of the existence of a
proportionality relationship between the oscillation frequency of
the fluid jet in the oscillation chamber and the flow rate of the
fluid along the pipe, the value of the fluid flow rate can be
deduced by measuring the oscillation frequency. The fluid jet
sweeps over the temperature sensor, thereby modifying its
temperature by heat exchange, and consequently measuring
temperature variations of the sensor by measuring variations in its
electrical resistance makes its possible to determine the
oscillation frequency of the jet.
[0011] The flowmeter preferably has two temperature sensors placed
in the cavity 17 between the obstacle 11 and the inlet 9,
symmetrically on either side of the inlet 9.
[0012] A duct 18 pierced by a hole is provided in the body of the
flowmeter to pass electrical connections between said body (and in
particular its sensor(s)), and a counter for informing the user of
parameters such as total consumption of fluid and fluid flow
rate.
[0013] Respective heat exchanges between the temperature sensor and
both the fluid and the body of the flowmeter are shown in FIG.
2.
[0014] The heat exchanges between the sensor and the oscillating
fluid are described by the following equation:
.PHI..sub.1=K.sub.1(T.sub.th-T.sub.g)
[0015] where:
[0016] .PHI..sub.1 is the power dissipated towards the oscillating
fluid;
[0017] K.sub.1 is the thermal conductance between the sensor and
the fluid;
[0018] T.sub.th is the temperature of the sensor; and
[0019] T.sub.g is the temperature of the oscillating fluid.
[0020] It should be observed that the thermal conductance K.sub.1
depends on the exchange area of the sensor, and on the thermal
conductivity, the density, and the speed of the fluid.
Consequently, when the fluid jet is oscillating, K.sub.1 depends on
time.
[0021] Heat exchanges between the sensor and the body of the
fluidic oscillator via the structure of the sensor and its
packaging are described by the following equation:
.PHI..sub.2=K.sub.2(T.sub.th-T.sub.b)
[0022] where:
[0023] .PHI..sub.2 is the power dissipated towards the body of the
fluidic oscillator;
[0024] K.sub.2 is the thermal conductance between the sensor and
the body of the fluidic oscillator;
[0025] K.sub.th is the temperature of the sensor; and
[0026] T.sub.b is the temperature of the body of the fluidic
oscillator.
[0027] It should be observed that the thermal conductance K.sub.2
is independent of fluid oscillations and consequently provides no
information useful in determining the oscillation frequency.
[0028] The principle of conservation of energy leads to the
following equation for describing the heat exchanges: 1 C T t h t +
K 1 ( t ) ( T t h - T g ) + K 2 ( T t h - T b ) = p ( t )
[0029] where:
[0030] C is the heat capacity of the sensor; and
[0031] p(t) is the instantaneous electrical power dissipated by the
sensor.
[0032] It has been observed that for a sensor powered with DC, as
is the case in prior art fluidic oscillator flowmeters, and under
well-specified temperature conditions corresponding to the
following: 2 T g - T b = V 2 4 K 2 R t h ,
[0033] where:
[0034] R.sub.th is the electrical resistance of the sensor,
information concerning the angular frequency .omega..sub.0 of the
oscillating fluid jet is lost because .delta.T.sub.th(t)=0.
[0035] Such temperature conditions can be encountered, for example,
when a hot fluid penetrates into a cold flowmeter. FIG. 3 shows how
the amplitude of the signal V.sub.m measured across the output
terminals of the temperature sensor varies as a function of time t.
It can be seen that under the above-specified temperature
conditions, the signal diminishes until it reaches a value where it
is no longer possible to measure the oscillation frequency of the
jet.
[0036] An object of the present invention is to propose a method of
measuring the oscillation frequency of a fluid jet in a fluidic
oscillator using a temperature sensor, which method is insensitive
to temperature conditions, and more particularly is insensitive to
transient stages in which, for example, a hot fluid penetrates into
a cold flowmeter.
[0037] According to the invention, this object is achieved by a
method of measuring the oscillation frequency of a fluid jet in a
fluidic oscillator using a temperature sensor whose resistance
varies as a function of the oscillation frequency f.sub.0 of the
jet, said method consisting in:
[0038] feeding the temperature sensor with an AC voltage of
frequency f; and
[0039] determining the frequency components around the frequency
3.times.f in the signal output by the temperature sensor in order
to determine the oscillation frequency f.sub.0 of the jet.
[0040] In a preferred implementation of the method of the
invention, the frequency components in the output signal from the
temperature sensor are determined by using the following steps:
[0041] measuring the resulting measurement signal V(t) across the
terminals of the temperature sensor;
[0042] synchronously demodulating the measurement signal at the
frequency 3.times.f; and
[0043] determining the frequency of the demodulated measurement
signal, which frequency corresponds to the oscillation frequency
f.sub.0 of the jet.
[0044] The step of synchronously demodulating the measurement
signal at the frequency 3.times.f is preferably performed by
multiplying the measurement signal V(t) by
cos(3.times.2.pi..times.f.times.t).
[0045] Other advantages and characteristics of the invention appear
on reading the following description made by way of example and
with reference to the accompanying drawings, in which:
[0046] FIG. 1 shows a prior art fluidic oscillator flowmeter, in an
exploded view;
[0047] FIG. 2 is a diagram of the respective heat exchanges between
the temperature sensor and both the fluid and the flowmeter
body;
[0048] FIG. 3 is a graph showing how the component at the frequency
f of the output signal from the temperature sensor varies when the
sensor is fed with DC during a temperature transition stage;
[0049] FIG. 4 is a diagram showing the circuit for biasing the
temperature sensor in the form of half a Wheatstone bridge;
[0050] FIGS. 5A and 5B show the frequency components of the output
signal from the temperature sensor when it is fed with DC and with
AC respectively;
[0051] FIG. 6 shows how the frequency component at 3f in the signal
output by the temperature sensor varies when the sensor is fed with
AC during a temperature transition stage; and
[0052] FIG. 7 is a diagram showing the various steps in a
particular implementation of the method of the invention.
[0053] When the sensor is fed with AC of amplitude v, the
instantaneous electrical power is given by the following
expression: 3 p ( t ) = v 2 R t h cos 2 ( t )
[0054] where:
[0055] R.sub.th is the electrical resistance of the sensor; and
[0056] .omega. is the angular frequency of the AC fed to the
sensor.
[0057] It is recalled that angular frequency is related to
frequency by the relationship .omega.=2.pi..times.f. Both concepts
are used interchangeably below.
[0058] Under such conditions, solving this equation gives a
solution of the form T.sub.th(t)=f(p(t), K.sub.1(t), K.sub.2,
T.sub.th, T.sub.b), which can be approximated by a method of
perturbations which leads to a temperature response in AC mode as
follows:
.delta.T.sub.th(t)=T.sub..omega.
cos(2.omega.t+.phi.)+.epsilon.T.sub..omeg- a.A
cos((2.omega.+.omega..sub.0)t+.phi..sub.A)+.epsilon.T.sub..omega.B
cos((2.omega.-.omega..sub.0)t+.phi..sub.B)+.epsilon.T.sub..omega.C
sin((.omega..sub.0t+.phi..sub.C)
[0059] where:
[0060] .omega..sub.0 is the angular frequency of the oscillating
fluid jet,
[0061] and where 4 T = P a c ( K 1 + K 2 ) 2 + ( 2 C ) 2 a n d sin
( ) = - 2 C ( K 1 + K 2 ) 2 + ( 2 C ) 2 T A = K 1 T 2 C 2 ( 2 + 0 )
2 + ( K 1 + K 2 ) 2 a n d sin ( A ' ) = C ( 2 + 0 ) C 2 ( 2 + 0 ) 2
+ ( K 1 + K 2 ) 2 w i t h A = + - A ' T B = K 1 T 2 C 2 ( 2 + 0 ) 2
+ ( K 1 + K 2 ) 2 a n d sin ( B ' ) = C ( 2 - 0 ) C 2 ( 2 - 0 ) 2 +
( K 1 + K 2 ) 2 w i t h B = + - B ' T C = K 1 K 1 + K 2 K 2 ( T g +
T b ) - P a c C 2 0 2 + ( K 1 + K 2 ) 2 a n d sin ( C ) = - C 0 C 2
0 2 + ( K 1 + K 2 ) 2 a n d P a c = V 2 8 R
[0062] represents the electrical power dissipated in the
temperature sensor.
[0063] Solution consists in using temperature components which do
not cancel regardless of the oscillator temperature T.sub.b and the
fluid temperature T.sub.g.
[0064] To convert the temperature response into a usable electrical
signal, it is possible to use a half Wheatstone bridge circuit as
shown in FIG. 4. The sensor of resistance R.sub.TH in series with a
resistor R of known resistance is biased by an AC voltage V.sub.p.
The measurement voltage V.sub.m is taken across the terminals of
the sensor of resistance R.sub.TH. The frequency components of this
voltage are analyzed so as to determine the angular frequency
.omega..sub.0 of the oscillating fluid jet, or its frequency
f.sub.0.
[0065] FIGS. 5A and 5B show the frequency components of the output
signal from the temperature sensor when it is powered with DC as in
the prior art and with AC as in the invention, respectively.
[0066] When the sensor is powered with DC, frequency analysis
reveals clearly only one component at f.sub.0. As explained above,
there exist certain temperature conditions for which this component
is of zero amplitude.
[0067] When the sensor is fed with AC, frequency analysis reveals
frequency components depending on f.sub.0 located at f-f.sub.0,
f+f.sub.0, 3f-f.sub.0, 3f+f.sub.0. It has been observed (see FIG.
6) that the components at 3f-f.sub.0 and 3f+f.sub.0 never cancel
out regardless of the temperature of the oscillator body T.sub.b
and of the fluid jet T.sub.g.
[0068] The table below gives the frequency components of the
voltage output from the half Wheatstone bridge when the sensor is
fed with an AC voltage.
1 Components of Vm(t): .omega. - .omega..sub.0 5 T V 32 [ T C cos (
( - 0 ) t - C ) + T B cos ( ( - 0 ) t + B ) .omega. 6 V 2 cos ( t )
+ T P ac V 4 ( K 1 + K 2 ) 2 + ( 2 C ) cos ( t + ) .omega. +
.omega..sub.0 7 T V 32 [ T C cos ( ( + 0 ) t + C ) + T A cos ( ( +
0 ) t + A ) ] 3.omega. - .omega..sub.0 8 T V 32 T B cos ( ( 3 - 0 )
t + B ) 3.omega. 9 T P ac V 4 ( K 1 + K 2 ) 2 + ( 2 C ) 2 cos ( 3 t
+ ) 3.omega. + .omega..sub.0 10 T V 32 T A cos ( ( 3 + 0 ) t + A
)
[0069] using the various parameters whose expressions are given
above.
[0070] FIG. 7 is a diagram showing the various steps of the method
in a particular implementation of the invention.
[0071] The temperature sensor is fed with an AC voltage of
frequency f.
[0072] The first step 20 consists in measuring the measurement
signal V.sub.m(t) across the terminals of the temperature sensor.
Frequency analysis reveals frequency components depending on
f.sub.0 located at f-f.sub.0, f+f.sub.0, 3f-f.sub.0,
3f+f.sub.0.
[0073] The second step 22 consists in isolating the frequency
component of 3f+f.sub.0, which component never cancels out whatever
the temperature of the oscillator body T.sub.b and of the fluid jet
T.sub.g. This step is performed by synchronously demodulating the
measurement signal at the frequency 3.times.f. In practice, the
step of synchronously demodulating the measurement signal at the
frequency 3.times.f consists in multiplying the measurement signal
V(t) by cos(3.times.2.pi..times.f.times.t). This operation serves
to shift the spectrum into so-called "base" band.
[0074] The third step 24 consists in determining the frequency of
the demodulated measurement signal, which frequency corresponds to
the oscillation frequency f.sub.0 of the jet. In practice, this
step is performed by counting the number of periods in the
demodulated measurement signal over a given length of time.
[0075] Advantageously, prior to the step of determining the
frequency of the measurement signal, the demodulated measurement
signal is filtered by means of a lowpass filter so as to eliminate
undesirable frequency components introduced during the synchronous
demodulation step.
[0076] In the context of laboratory measurements, it should be
observed that the method as a whole can be considerably simplified
since under such circumstances additional calculation means are
available separate from those of the flowmeter. Such calculation
means enable the fast Fourier transform (FFT) of the signal
measured across the terminals of the temperature sensor to be
calculated. This calculation serves to isolate the various
frequency components of interest, and in particular it makes it
possible to determine directly the value of the angular frequency
.omega..sub.0 and thus of the frequency f.sub.0 for the components
at 3f-f.sub.0 and/or 3f+f.sub.0.
[0077] These additional calculation means can be constituted, for
example, by a microcomputer whose energy consumption and size are
not compatible with a self-contained and compact flowmeter which
normally operates on batteries, which is why the fast Fourier
transform of the measured signal can be obtained only in the
context of use in a laboratory.
* * * * *